1. Field of the Invension
The present invention is directed to an extremely accurate axial adjusting means for objectives and other devices with extremely limited depth of focus which must be moved linearly with high precisions of the order of 0.4 micron resolution. The device particularly finds application for the movement of objectives in an X-ray lithography system used in the fabrication of semiconductors formed in silicon wafers. Objectives are used in the alignment and registration of wafers and fabrication masks so that a sequence of successive masks may very accurately be aligned, moved and gapped with respect to a wafer.
2. Description of the Prior Art
Heretofore, movement of the objectives has been by an appropriate gearing of lead-screw linear motors directly coupled to the objectives. These mechanisms are susceptible to backlash, are cumbersome, large, and not capable of long-term use for the accuracies being sought.